Extruded foam molded by extrusion-foaming a thermoplastic resin and an assembly of bundled threads of the extruded foam molded by a so-called strand-extrusion involving the steps of extruding the thermoplastic resin from dies having a large number of small pores; bundling extruded resin threads together; and fusing and foaming the surfaces thereof are excellent in mechanical properties even though light in weight. Therefore, the foam is broadly applied as structural materials in various fields, such as the fields of building construction, civil engineering and the fields of automobiles. In particular, the foam is expected to be employed as a structural material having an insulation efficiency and a sound absorption performance. As such extruded foam of a thermoplastic resin, extruded foam formed of a polystyrene-based resin is known. In addition, as extruded foam of a thermosetting resin, extruded foam formed of a polyurethane-based resin is known.
However, a polyurethane resin and a polystyrene resin are materials that are not always excellent in recycling characteristics, and there is a problem that when these resins are used, it is difficult to sufficiently comply with the construction waste recycling law (law on recycling of materials for construction works, etc.). In addition, the polystyrene resin has poor heat resistance and chemical resistance. Therefore, extruded foam made of a thermoplastic resin that is alternative to those resins has been demanded.
On the other hand, a polypropylene-based resin, which is excellent in mechanical property, heat-resisting property, chemical resistance, electrical property and the like, is also a low cost material, so that it is widely used in various molding fields. Thus, extruded foam of the polypropylene-based resin is also expected to have high industrial utility. In recent years, the extruded foam of the polypropylene-based resin has been expected to be an insulating material and a sound absorption material, and there have been a variety of studies conducted (e.g., Patent Document 1 and Patent Document 2).
Furthermore, in fields such as building construction, civil engineering or automobiles, there has been a need that the extruded foam has a vibration suppressive performance and a high shock-absorbing capability (energy-absorbing capability) in addition to the insulation efficiency and the sound absorption performance. For instance, the extruded foam, if applicable to a vibrating substrate surface such as a door panel, a fender panel, a ceiling panel, a trunk-lid etc., of an automobile, can also favorably reduce a weight of the automobile. For the extruded foam to be used in the ceiling, the door and the like of the automobile, the extruded foam is required to have a capability of absorbing a shock energy caused in an automobile collision and the like as well as a high sound absorption performance.
[Patent Document 1] JP-T-2002-524635
[Patent Document 2] JP-T-2003-528173